Negative dazzle reflex and optic neuropathy due to chronic glaucoma in a chinchilla: clinical evaluation and correlation with pathological findings

Purpose: The clinical evaluation of cranial nerve II func- tion in the chinchilla is challenging. It has been reported that the dazzle reflex is absent in the majority of normal chinchillas. The dazzle reflex was evaluated in a case of chronic unilateral glaucoma in a chinchilla and in normal controls to assess its usefulness in assessing visual path- ways disease. Methods: The left buphthalmic globe of a 2.5 years old female chinchilla was evaluated clinically and ultrasono- graphically (12 MHz linear probe; B mode). Dazzle reflex was tested in both eyes of the patient and in 11 normal chinchillas with Heine otoscope and slit lamp light at dif- ferent brightness, in light and dark adaptation, and pre- and post-pharmacological mydriasis. Following worsening of the uveitis the affected eye was enucleated and histology was performed. Results: Dazzle reflex was negative in the glaucomatous eye. The enlarged hypotonic (IOP OS 4, OD 14 mmHg) globe had anterior uveitis with anteriorly dislocated cata- ractous lens, following lens capsule rupture, and optic nerve atrophy. Ultrasonography confirmed the lesions. Histologically, zonal neutrophilic and macrophagic uveitis with sparse granulocytes within the cataractous lens, full thickness retinal atrophy and optic nerve spongiosis and gli- osis were confirmed. In all 23 normal eyes, dazzle reflexes were positive when tested in dark adapted, pharmacologi- cally dilated pupils. Conclusions: Since the dazzle reflex was evoked in all the normal eyes, its absence in the glaucomatous eye was sug- gestive of optic nerve atrophy as suspected during ophthal- moscopy. Dazzle reflex can be useful in the evaluation of chinchillas’ visual pathways.